Pad structure of semiconductor package

ABSTRACT

A pad structure for semiconductor package. A printed circuit board with solder lands formed on predetermined locations are provided. First circular pad portions are formed protruding laterally on upper surfaces of the solder lands. Second circular pad portions are formed protruding laterally from other lateral sides of the pads. The leads are secured to the pads of the semiconductor package so that when the first and second circular pad portions are pushed laterally, the circular pad portions do not contact each other, preventing short circuits.

CLAIM OF PRIORITY

[0001] This application makes reference to, incorporates the sameherein, and claims all benefits accruing under 35 U.S.C. §119 from myapplication PAD STRUCTURE OF SEMICONDUCTOR PACKAGE filed with the KoreanIndustrial Property Office on Jul 20, 1999 and there duly assignedSerial No. 29391/1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to semiconductor packages,specifically to semiconductor packages with pad structures formed onPrinted Circuit Boards (PCBs) improved to prevent short circuits.

[0004] 2. Description of the Prior Art

[0005] Generally, a semiconductor package comprises a semiconductor bodyand a plurality of leads extending from the semiconductor. Suchsemiconductor packages are secured to a PCB by such methods assoldering.

[0006] Recently, as the number of leads extending from the semiconductorhas increased due to a high degree of integration, the spacing betweenthe leads has tended to become shorter. As the spacing between the leadsdecreases, short circuits caused by contacts between the leads occurmore frequently. Therefore, it is necessary to secure a plurality ofleads with small spacing onto the PCB effectively.

[0007] A typical semiconductor package comprises a semiconductor bodyand a plurality of leads extending from both sides of the semiconductorbody. On the PCB at locations corresponding to the leads, a plurality ofpads are formed. At the middle portion of the pad, a squared pad portionis formed. When securing the package onto the PCB, the leads aresoldered to the engaging portions 6 and the squared pad portions.

[0008] However, when the lead is attached to the pad, the squaredportions of the pad protrude laterally, forming a contact portionabutting with the squared portion of the adjacent pad. Hence, causingshort circuits which deteriorate the performance of the semiconductor.

[0009] Generally, flatness of the pad is maintained within 80 to 100 μm.The lead is attached to the pad uniformly when such flatness ismaintained. However, when the end portions of the connectors and leadsof a quad flat pack (QFP) are raised upward for a predetermined heightrendering the flatness in excess of 150 μm, the lead may float or theleads may not be attached to the pad properly. This may also causeinadequate tensile strength.

[0010] Furthermore, since the squared pad portion is formed at themiddle portion of the pad, the lead tends to be fused only to bothlateral sides of the middle portions of the lead. Therefore, when thelead is not maintained horizontal within predetermined degree, theforward or rear portion tends to float with only the middle portionbeing attached, reducing the tensile strength.

SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to provide animproved pad structure for a semiconductor package.

[0012] It is a further object of the invention to provide a padstructure which is resistant to the formation of short circuits betweenthe leads during soldering.

[0013] It is a yet further object of the invention to provide a padstructure which has an increased tensile strength.

[0014] It is a still further object of the invention to provide a padstructure which prevents floating of the leads even if the leads areperfectly flat.

[0015] The above and other objects, advantages and features of thepresent invention will become more readily appreciated and understoodfrom a consideration of the following detailed description of apreferred embodiment of this invention when taken together with theaccompanying drawings.

[0016] In order to achieve above objects, a pad structure for asemiconductor package according to the present invention comprises: aprinted circuit board with solder lands formed on predetermined portionsthereof; and a plurality of pads formed on upper surface of the solderlands to which a plurality of leads of the semiconductor package isattached, a first circular pad portions protruding laterally fromlateral sides of the pads, second circular pad portions protrudinglaterally from other lateral sides of the pads, wherein the leads aresecured to the pads of the semiconductor package so that when the firstand second circular pad portions are pushed laterally, the circular padportions do not contact each other which prevents short circuits.

[0017] Preferable, heights of the first and the second circular padportions are identical to heights of the pads, the first and secondcircular pad portions protruding upward for a predetermined height dueto surface tension, raising the height of the pad when the leads aresecured to the pads, the leads depressed for a predetermined depth andthen bonded so that the leads are secured to the pads even when theleads are not horizontal.

[0018] More preferably, the first and second circular pads are fused toboth lateral sides of the leads, resisting force exerted in lateraldirections when the leads are secured to the pads.

[0019] In order to achieve above objects, a pad structure for asemiconductor package according to the present invention may comprise: aprinted circuit board with solder lands formed on predetermined portionsthereof, and a plurality of pads formed on upper surface of the solderlands, first pads with circular pad portions formed on predeterminedlocations thereof, second pads with circular pad portions disposed inalternating manner with respect to the circular pad portions of thefirst pads formed on predetermined locations thereof, said first padsand the second pads continuously repeated on the pads, wherein the leadsare secured to the pads so that when the first and second circular padportions are pushed laterally, the circular pad portions do not contacteach other whereby short circuits are prevented.

[0020] Preferably, heights of the first and the second circular padportions are identical to heights of the pads, the first and secondcircular pad portions protruding upward for a predetermined height dueto surface tension raising the height of the pad when the leads aresecured to the pads, the leads depressed for a predetermined depth andthen bonded so that the leads are secured to the pads even when theleads are not horizontal.

[0021] More preferably, the first and second circular pads are fused toboth lateral sides of the leads, resisting force exerted in lateraldirection when the leads are secured to the pads.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A more complete appreciation of the invention, and may of theattendant advantages, thereof, will be readily apparent as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings in which like reference symbols indicate the same or similarcomponents, wherein:

[0023]FIG. 1 is a perspective view showing a typical semiconductorpackage attached to the PCB;

[0024]FIG. 2 is a plan view schematically showing portion “A” of FIG. 1;

[0025]FIG. 3 is a sectional view showing a typical floating lead of thesemiconductor package;

[0026]FIG. 4 is a perspective view showing a semiconductor packageaccording to a preferred embodiment of the present invention attached tothe PCB;

[0027]FIG. 5 is a plan view schematically showing portion “A” of FIG. 4;

[0028]FIG. 6 is a lateral sectional view showing the lateral section ofa preferred embodiment of a pad according to the present invention;

[0029]FIG. 7 is a side view showing an initial stage of attaching thelead of the semiconductor package onto an upper surface of the padaccording to the present invention;

[0030]FIG. 8 is a side view showing the lead of the semiconductorpackage after attaching it to the upper surface of the pad;

[0031]FIG. 9 is a sectional view cut along line IX-IX of FIG. 8;

[0032]FIG. 10 is a sectional view cut along line X-X of FIG. 8;

[0033]FIG. 11 is a plan view showing pads according to anotherembodiment of the present invention;

[0034]FIG. 12 is a sectional view taken along line XII-XII of FIG. 11;

[0035]FIG. 13 is a side view showing a lead of a semiconductor packagebefore securing it to the pad;

[0036]FIG. 14 is a side view showing the lead of the semiconductorpackage after securing it to the pad;

[0037]FIG. 15 is a sectional view taken along line XV-XV of FIG. 14; and

[0038]FIG. 16 shows the process of forming a pad according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0039] Turning now to the drawings, FIG. 1 is an exploded perspectiveview of a semiconductor package secured to a PCB. FIG. 2 is a plan viewshowing the “A” portion of FIG. 1, as discussed above.

[0040] As can be seen in the drawing, the semiconductor package 1comprises a semiconductor body 2 and a plurality of leads 3 extendingfrom both sides of the semiconductor body 2. On the PCB 4 at locationscorresponding to the leads 3, a plurality of pads 5 are formed. At themiddle portion of the pad 5, a squared pad portion 7 is formed. Whensecuring the package 1 onto the PCB 4, the leads 3 are soldered to theengaging portions 6 and the squared pad portions 7.

[0041] However, when the lead 3 is attached to the pad 5, the squaredportions 7 of the pad 5 protrude laterally, forming a contact portion 8abutting with the squared portion of the adjacent pad. Hence, causingshort circuits which deteriorate the performance of the semiconductor.

[0042] Generally, flatness of the pad 5 is maintained within 80 to 100μm. The lead 3 is attached to the pad 5 uniformly when such flatness ismaintained. However, as illustrated FIG. 3, when the end portions 3 a ofthe connectors and leads 3 of a quad flat pack (QFP). are raised upwardfor a predetermined height rendering the flatness to exceed 150 μm, thelead 3 may float or the leads may not be attached to the pad 5 properly.This may also cause inadequate tensile strength.

[0043] Furthermore, since the squared pad portion 7 is formed at themiddle portion of the pad 5, 8 the lead tends to be fused only to bothlateral sides of the middle portions of the lead 3. Therefore, when thelead is not maintained horizontal within predetermined degree, theforward or rear portion tends to float with only the middle portionbeing attached, reducing the tensile strength.

[0044] The present invention will now be described in detail referringto the accompanying drawings. However, the embodiments hereinafterdescribed should be interpreted as illustrative and in no senselimiting.

[0045]FIG. 4 is an exploded perspective view showing a semiconductorpackage according to the present invention attached to a PCB. As can beseen in the drawing, the semiconductor package 10 comprises a body 12and a plurality of leads 13 extending from the body 12. A plurality ofsolder lands are formed on locations of the PCB 14 corresponding to thelocation of the lead 13. A plurality of pads 15 are formed on upperportions of the solder lands. Such pads are referred to as ProjectionSolder (“P.S.”) pads which will be simply termed pads hereinafter.

[0046] As can be seen in FIGS. 5 & 6, pads 15 and 15 a are rectangularand formed on the PCB with a predetermined thickness by a mask process.Circular pad portions 17 are each formed on predetermined locations ofthe pads (15, 15 a). Bonding regions 16, to which leads are attached,are on the upper surface of the pads. Spacing t1 between the pads 15 and15 a is decided according to the spacing between the leads 13 (refer toFIG. 4) of the semiconductor package 10. In actual product, the spacingranges from approximately 0.4 mm to 0.65 mm.

[0047] At predetermined locations of the lateral sides of the pad 15,the first and second circular pad portions 17 & 18 are formed protrudingin lateral direction in a zigzagged manner. In the embodiment shown,these take the form of semicircular protrusions from diagonally oppositesides of pad. The first and second circular pad portions 17 & 18protrude for a predetermined length t2, preferably ranging fromapproximately 0.065 mm to 0.1 mm according to the spacing between thepads 15.

[0048] Short circuits are prevented since circular pad portions of thepad 15 a are prevented from contacting each other, or the circular padportions of pad 15, even when the first and second circular pad portions17, 18 are pressed in lateral direction by the lead 13 (refer to FIG.4).

[0049] Furthermore, since heights of the first and second circular padportions 17, 18 are the same as the height of the pad 15, the circularpad portions can abut the lower surface of the lead 13 in a uniformmanner.

[0050]FIG. 7 is a side view showing an initial stage of attaching thelead of the semiconductor package on an upper surface of the padaccording to the present invention and FIG. 8 is a side view showing thelead of the semiconductor package after attaching it to the uppersurface of the pad. As can be seen in the drawings, heat is applied tothe pad 15 when attaching the lead 13 to the pad 15. When the pad isturned into liquid having certain viscosity, the lead 13 is moveddownward, the lower surface 13 a of the lead 13 approaching the uppersurface 15 a of the pad 15.

[0051] When the lower surface 13 a of the lead 13 approaches the upperside 15 b of the pad, upper portions of the first and second circularpad portions 17 & 18 rises upward as the solder melts. Since the firstand second circular pad portions 17 & 18 are circular, solder isconcentrated to the center part of the of the first and second circularpad portions 17 & 18 due to surface tension. That is, the solder wellsup forming meniscuses 17 a and 18 a. Therefore, as the lead 13 graduallydescends, solder of the first and second circular pad portions 17 and18, along with the solder between pad portions 17 and 18, concentratesin the direction of the first and second pad portions 17 & 18, resultingin a sufficient rise of the pad 15 to depress (sink) the lead 13 withinthe solder of the first and second pad portions.

[0052] Therefore, as can be seen in FIG. 8, when the lead 13 iscontinuously moved downward and settles on the upper surface 15 b of thepad 15, the lower surface 13 a of the lead 13 is depressed, that is,partially submerged, within the upper surface 15 a of the pad 15.Therefore, the lead 13 can be firmly attached even when it is notperfectly horizontal.

[0053] Furthermore, the first and second pad portions 17 & 18 are pushedto both sides and fused to both side surfaces 15 b & 15 c (refer to FIG.10) of the lead 13. Therefore, the lead 13 abuts the pad 15 in anuniform manner and increases tensile strength thereof since both sidesare supported.

[0054] On the other hand, after attaching the semiconductor package 10to the PCB 14 according to afore-said procedure, the PCB goes through aheating device such as a heater. During such process, the pad 15 meltsand adhesion of the solder between the leads and the pads becomesuniform.

[0055]FIG. 9 is a sectional view cut along line IX-IX of FIG. 8, andFIG. 10 is a sectional view cut along line X-X of FIG. 8.

[0056] As can be seen in the drawings, once the leads are settled on thepads 15, the upper surfaces 15 b of the pads 15 uniformly contact thelower surfaces 13 a of the leads 13. Also, the first circular padportion 17 (refer to FIG. 5) is pushed laterally by the force exerted bythe lead 13 and is bonded to a first side surface 15 b of the lead 13,forming a first fused portion 17 a. Therefore, a lateral load of thelead 13 is resisted.

[0057] Furthermore, the second circular pad portion 18 is also pushedlaterally by the force exerted by the lead 18 and a second fused portion18 a is formed by bonding it to a second side surface 18 a. Therefore,loads applied to the lead 13 in both lateral directions are supported bythe first and the second circular pad portions 17 & 18. Therefore, thetensile strength of the lead and the pad is enhanced.

[0058] Another preferred embodiment according to the present inventionis shown in FIG. 11. The difference in this preferred embodiment lies inthe shape of the circular pad portion. That is, on predeterminedlocation of the pads 55 and 65 are formed circular pad portions 57 and58. Two circular pad portions are formed laterally opposite each otheron each pad. Thus, the circular pad portions 57 of pad 55 define arounded region 61 as bounded by dotted line 60 in FIG. 11. Regions 56indicates the regions of the pads where the leads will be attached.

[0059] The circular pad portions 57 and 58 of the pads 55 and 65 aredisposed in a zigzagged manner. That is, they are disposed alternatelytoward opposite ends of adjacent pads, in zig-zag fashion along a lineof pads. This arrangement can also be considered to be an alternatingantiparallel arrangement of pads having the shape of pad 55.

[0060] Since the first and the second circular pad portions 57, 58 aredisposed in a zigzagged manner, they do not contact each other even whenthe lead 53 is pressed in lateral direction, preventing short circuits.

[0061] As can be seen in FIG. 12, height of circular pad portions 57,and region 61, are maintained identical to that of pad 55 so that thepad can maintain uniform contact with the lower surface 53 a (refer toFIG. 14) of the lead 53.

[0062] As can be seen in FIG. 13 and 14, heat is applied to the pad 55when attaching lead 53 to the pad 55. During the heating, the pad 55turns into a liquid having certain viscosity and by moving the lead 53downward, the lower surface 53 a of the lead 53 approaches the uppersurface 55 a of the pad 55.

[0063] When the lower surface 53 a of the lead 53 approaches the uppersurface 55 a, attracting force tends to raise the pad 55 upward. Duringsuch an action, solder concentrates at a center portion of the region 61between circular pad portions 57 due to surface tension. Therefore, theupper end portions of the pad 55 and the circular pad portions 57 riseupward for a predetermined length t1, contacting the lower surface ofthe lead 53.

[0064] As can be seen in FIG. 14 and 15, when the lead 53 constantlymoves downward and settles on the upper surface 55 a of the pad 55, thelower surface 53 a of the lead 53 makes uniform contact with the uppersurface of the pad 55 and is depressed therein to a predetermined depth.The circular pad portions 57 are pushed to both sides of the lead 53.The circular pad portions 57 pushed to the sides are fused to both sides53 b of the lead 53, resisting the force exerted to the lead in lateraldirection.

[0065] The circular pad portions 57 and 58 of the pads 55 and 65 aredisposed in a zigzagged manner so that both sides 53 b of the lead arefused, thereby supporting the lead 53 in zigzagged shape. That is, thecircular pad portions are formed on the sides of the pads towardopposite ends of the pads on alternate pads. This yields a zigzagpattern along a row of pads. Therefore, the lead 53 resists the loadapplied in lateral direction.

[0066] Furthermore, even when the lead 53 is not horizontal and the endportion 53 a of the lead 53 is raised, the lead 53 is depressed withinthe pad 55 under predetermined depth so that floating or non-contactingof the pad 55 does not occur when the raised height t4 of the lead 53 iswithin the raised height t3 of the circular pad portion 57. Since thelead 53 makes uniform contact with the pad 55, the tensile strength isenhanced.

[0067] After attaching the semiconductor package 50 onto the PCB 54, thePCB 54 goes through heating equipment such as a heater, during which thepad 55 melts to make the soldering between the pad 55 and the lead 53uniform.

[0068] Hereinafter, steps for attaching the semiconductor according to apreferred embodiment of the present invention will be discussed in moredetail. Referring to FIG. 16, solder lands are formed on the PCB 14using such methods as etching. Then, pads 15 are formed on upper surfaceof the solder lands using a metal mask 20. That is, a plurality ofopened portions 21 are perforated on the metal mask 20 at locationscorresponding to the locations of the pads 15. Therefore, a plurality ofopened portions 21 having identical shape as that of the pads 15 areformed on the metal mask 20.

[0069] After placing the metal mask 20 on the PCB 14, solder cream isdeposited on the metal mask 20. Then the metal mask 20 is removed. Sincesolder cream remains on the opening portions 21, a plurality of pads areformed.

[0070] As can be seen in FIGS. 4 to 10, the pad 15 is heated and turnedinto liquid having certain viscosity. Then the lead 13 of thesemiconductor package 10 is settled on the upper surface of the pad 15.Here, the first and second circular pad portions 17 & 18 protrudesupward for a predetermined length due to surface tension, contacting thelower surface of the lead 13.

[0071] In this state, the lead 13 is pressed downward so that the uppersurface 13 a of the lead 13 is distributed uniformly on the uppersurface 15 a of the pad 15. The first and second circular pad portions17, 18 are pushed in lateral direction and fused to the first and secondside surfaces 17 a, 18 a of the lead 13. Here, since the first andsecond pad portions 17, 18 are shaped in a zigzagged manner, both sidesof the lead 13 are supported in a zigzagged manner. Therefore, the lead13 resists to load in lateral direction.

[0072] Since the PCB 14 is heat treated by passing the heater, fusingbetween the pad 15 and the lead 13 becomes more uniform. This means thatthe lead 13 and the pad 15 are secured in a uniform manner, resisting tostronger vertical and lateral loads.

[0073] As stated above, the pad is disposed in a zigzag manner,preventing the contact between the adjacent pads which causes shortcircuits.

[0074] Furthermore, since a plurality of circular pad portions supportboth lateral sides and lower surface of the leads in a zigzag manner,the deviation of the leads from horizontal form or misplacement of amounter can be compensated, which raises tensile strength between thepads and the leads.

What is claimed is:
 1. A pad structure for a semiconductor package,comprising: a printed circuit board with solder lands formed onpredetermined portions thereof; and a plurality of pads formed on uppersurface of the solder land to which a plurality of leads of thesemiconductor package are attached, a first circular pad portionsprotruding laterally from lateral sides of the pads, second circular padportions protruding laterally from other lateral sides of the pads,wherein the leads are secured to the pads of the semiconductor packageso that when the first and second circular pad portions are pushedlaterally, the circular pad portions do not contact each other wherebyshort circuits are prevented.
 2. The pad structure of claim 1, whereinheights of the first and the second circular pad portions are identicalto heights of the pads, the first and second circular pad portionsprotruding upward for a predetermined height due to surface tension,raising the height of the pad when the leads are secured to the pads,the leads depressed for a predetermined depth and then bonded so thatthe leads are secured to the pads even when the leads are nothorizontal.
 3. The pad structure of claim 2, wherein the first andsecond circular pads are fused to both lateral sides of the leads,resisting force exerted in lateral direction when the leads are securedto the pads.
 4. A pad structure for a semiconductor package, comprising:a printed circuit board with solder lands formed on predeterminedportions thereof; and a plurality of pads formed on upper surface of thesolder land, first pads with circular pad portions formed onpredetermined locations thereof, second pads with circular pad portionsdisposed in alternating manner with respect to the circular pad portionsof the first pads formed on predetermined locations thereof, said firstpads and the second pads continuously repeated on the pads, wherein theleads are secured to the pads so that when the first and second circularpad portions are pushed laterally, the circular pad portions do notcontact each other whereby short circuits are prevented.
 5. The padstructure of claim 4, heights of the first and the second circular padportions are identical to heights of the pads, the first and secondcircular pad portions protruding upward for a predetermined height dueto surface tension, raising the height of the pad when the leads aresecured to the pads, the leads depressed for a predetermined depth andthen bonded so that the leads are secured to the pads even when theleads are not horizontal.
 6. The pad structure of claim 5, wherein thefirst and second circular pads are fused to both lateral sides of theleads, resisting force exerted in lateral direction when the leads aresecured to the pads.
 7. A pad structure for receiving a lead of asemiconductor package, comprising: a printed circuit board; a firstsolder land formed on the printed circuit board; a first pad made ofsolder formed on said solder land, said first pad having a generallyrectangular shape of a predetermined flatness, said first pad furthercomprising: a first circular pad portion of the same height as the pad,protruding from a longer edge of the pad.
 8. The pad structure of claim7, further comprising: the flatness of said pad being in the range ofapproximately 80 to 100 μm.
 9. The pad structure of claim 7, furthercomprising: a second circular pad portion formed on the first pad on theopposite edge of the first pad from, and diagonally arranged to, thefirst circular pad portion.
 10. The pad structure of claim 9, furthercomprising: a second solder land adjacent to said first solder land; asecond pad having circular pad portions, of the same shape as said firstpad, formed on the second solder land, said second pad being orientedparallel to said first pad, and the edges of said first and second padsbeing spaced by a predetermined distance.
 11. The pad structure of claim9, further comprising: said first and second circular pad portionsprotruding from the edges of the first pad by in the range ofapproximately 0.065 to 0.1 mm.
 12. The pad structure of claim 10,further comprising: the predetermined distance between said first andsecond pads being in the range of approximately 0.4 to 0.65 mm.
 13. Thepad structure of claim 10, further comprising: a plurality of solderlands and pads arranged in a pattern to receive leads of a quad flatpack, each of said plurality of pads having the shape of said first pad.14. The pad structure of claim 7, further comprising: a second circularpad portion formed on the first pad on the opposite edge of the firstpad from, and laterally opposite to, the first circular pad portion. 15.The pad structure of claim 14, further comprising: a second solder landadjacent to said first solder land; a second pad having circular padportions, of the same shape as said first pad, formed on the secondsolder land, said second pad being oriented antiparallel to said firstpad, and the edges of said first and second pads being spaced by apredetermined distance.
 16. The pad structure of claim 15, furthercomprising: a third solder land adjacent to said second solder land; athird pad having circular pad portions, of the same shape as said firstpad, formed on the third solder land, said third pad being orientedantiparallel to said second pad, and the edges of said second and thirdpads being spaced by said predetermined distance.
 17. The pad structureof claim 16, further comprising: said first and second circular padportions protruding from the edges of the first pad by in the range ofapproximately 0.065 to 0.1 mm.
 18. The pad structure of claim 16,further comprising: the predetermined distance between said first andsecond pads being in the range of approximately 0.4 to 0.65 mm.
 19. Thepad structure of claim 16, further comprising: a plurality of solderlands and pads arranged in a pattern to receive leads of a quad flatpack, each of said plurality of pads having the shape of said first pad;and said plurality of pads arranged alternately antiparallel along a rowof leads.
 20. A method of attaching leads of a semiconductor package toa printed circuit board, comprising the steps of: forming pads on solderlands of the printed circuit board in the arrangement of the leads ofthe semiconductor package, each pad having a generally rectangular shapewith two protruding circular pad portions on opposite long sides of thepad; heating the pads while lowering the leads of the semiconductor ontothe pads; contacting the bottom surface of each lead of thesemiconductor with the solder welling up over the protruding circularpad portions until the solder flows so as to partially submerge the leadin the pad.
 21. The method of claim 20, further comprising: initiallyforming the pads on the solder lands by placing a metal mask having theshapes of the pads over the printed circuit board and applying soldercream to the mask.
 22. The method of claim 20, further comprising: aftersaid contacting step, heat treating the printed circuit board using aheater.
 23. The method of claim 20, further comprising: said twoprotruding circular pad portions being oriented diagonally opposite eachother.
 24. The method of claim 20, further comprising: said twoprotruding circular pad portions being oriented laterally opposite eachother, and each pad being oriented antiparallel to the pad adjacent toit.
 25. The method of claim 20, further comprising: said semiconductorpackage being a quad flat pack.